A safety valve is a mechanical device which may release pressure in a steam boiler, etc., when it becomes too great. Accordingly, many kinds of safety valves have been developed, but none of them can lead to entirely satisfactory results.
With reference to FIGS. 1 and 2, there are shown a prior art safety valve and a feeding water machine with the prior art safety valve, respectively. As illustrated, the safety valve (6) comprises an inlet (60) at the left side with respect to FIG. 2 and an outlet (61) communicated with the inlet (60). At the end of the inlet (60) there is a spring-loaded ball valve (63) which, upon receiving pressure greater than a predetermined value, will be opened. Consequently, the safety valve (6) will release pressure when it becomes too great. However, the safety valve (6) has the following drawbacks:
1. When the end of the pipe (not shown) connected with the outlet (61) is closed, the pressure inside the safety valve (6) as a consequence will be abruptly increased and so the safety valve will be opened to let water flow out of the outlet (66) so as to release the water pressure therein. Nevertheless, the compressor (50) of the feeding water machine (5) will continue to run even if the end of the pipe connected with the outlet (61) is closed, thereby wasting much energy.
2. To stop the feeding water machine for any significant period of time, it is necessary to first close the end of the pipe (not shown) connected with the outlet (61) of the safety valve (6) and then to switch off the feeding water machine (5). Furthermore, it is necessary to manually open the piping (not shown) connected with the outlet (61) so as to release the pressure therein; otherwise, the high pressure upstream of the valve will maintain pressure inside the feeding water machine and may expedite the aging of the packings (not shown) mounted in the feeding water machine (5) .